Test

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Chapter 8- Stoichiometry

Big, Scary name….Just calculations

chemists do!

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Quantitative Analysis

Composition stoichiometry- mass relationships of elements in compounds.

Reaction Stoichiometry- involves mass relationships between the reactants and products in reactions

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What do the coefficients mean?

Mole Ratios

Coefficients indicate the amount of each material (Moles or molecules) present in a reaction.

C6H12O6 + 6O2 6CO2 + 6H2O

So… when looking at a balanced equation we can derive a whole set of conversion factors!

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Mole Ratio- The Definition…

A conversion factor that relates the amounts in moles of any two substances involved in a chemical reaction.

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Go to the WS

Finish the back for HW

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You will be working in groups of 3- be sure to exchange contact info and be sure to communicate if you will be absent.

Jobs Rotate- Write you job at the top of each lab.1. Leader- Keeps all on task and makes sure directions are followed.2. Scientist- Follows directions and is in charge of making sure no mistakes occur.3. Mathematician- insures calculations are correct.

I will pick one lab per group to grade-- you get whatever score they get…make sure everyone in

your group is completing the lab!

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Copper Series- Lab ConcernsUse the same scales for each lab… they mass slightly

different.

Be sure to record any lab mistakes… too much reactant, lost product, other booboos.

You will be calculating percent error and trying to explain the errors.

You may never say that you made a mistake in your calculations-- there are 3 of you working, there

should be no mistakes!

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Copper Series- Lab 1

Write and balance the equation for the reaction of copper (Cu) plus nitric acid (HNO3) to produce Copper (II) nitrate (Cu(NO3)2) plus water (H2O) and nitrogen dioxide (NO2).

Procedure- Using the sharpie.. Put your period and lab station on the beaker. Ex: 2-1

1.Determine the mass of your empty beaker.

2.Determine the mass of the copper.

3.Send your scientist to the stock room to put 20mL of HNO3 into the beaker

4.Put on the watch glass and place on the hot plate in the fume hood.

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Warm Up:Mole to Mole Calculations….

Fe2O3 + 3CO 2Fe + 3CO2

1. How many mol CO are necessary to react with 2.2 mol Fe2O3?

2. How many mol Fe are produced if 1.8 mol CO is used?

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Fe2O3 + 3CO 2Fe + 3CO2

1. How many mol CO are necessary to react with 2.2 mol Fe2O3?

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Mole Ratios

Fe2O3 + 3CO 2Fe + 3CO2

b) How many mol Fe are produced if 1.8 mol CO is used?

How did you do on HW?

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Moles of A Moles of BMass of A Mass of B

Number of particles of A Number of particles of B

Volume of gaseous A Volume of gaseous B

The following chart summarizes the conversions we can do:

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So, can we use stoichiometry to determine the amount of product made in types of reactions lab?

We used 0.2 g of CuCO3 in the decomposition reaction.

How much CuO was produced?

CuCO3 CuO + CO2

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Can we determine the amount of magnesium oxide (g) were produced

in the synthesis reaction?

We used about 0.5 g of Mg.

Mg + O2 MgO

a. Balance the equation.

b. Place the mass of Mg used in the upper left.

c. Use DA to determine the theoretical mass of MgO.

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Important Vocabulary Terms

Theoretical yield- the maximum amount of product that can be produced from a given amount of reactant.

Actual Yield- measured amount of a product obtained from a reaction (in lab).

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What is the theoretical yield (in grams) of both products in the following reaction if 2.5 g of HCl is used?

Zn + HCl ZnCl2 + H2

a. Balance the equation

b. Put 2.5g HCl in the upper left

c. Solve for g of zinc chloride.

d. Solve for g of hydrogen.

Let’s make sure you are doing the lab calculations correctly.

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On your copper lab, #5 asks you to determine the theoretical yield for Cu(NO3)2. Do the calculation using the mass determined in #1.

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Copper Lab- Series 2

1. Obtain the mass of your Cu(NO3)2

2. Add about 20 ml of distilled water.

3. Add 30 ml of NaOH

4. Obtain the mass of your filter paper!!!

5. Filter the mixture- rinse it well with distilled water.

6. Wash out your original beaker (check to be sure it is still marked with your period and lab station.)

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Warm Up- Friday 2/8

Sodium reacts with Magnesium carbonate.

a.Write the reactants and predict the products.

b.How much magnesium is produced when 3.6 g of sodium reacts with excess MgCO3?

c.How much MgCO3 is needed to react with exactly 3.6g of Na?

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There are a bunch of other calculations we can do using the flow chart…

Moles of A Moles of BMass of A Mass of B

Number of particles of A Number of particles of B

Volume of gaseous A Volume of gaseous B

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Stoichiometric Conversions

How many grams of oxygen are produced when 17.5g of H2O2 decompose according to the following equation?

H2O2 H2O + O2

(Don’t forget to balance the equation!)

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Volume to Volume Calculations

How many liters of water are produced when 3.0L of Hydrogen react with excess oxygen?

H2(g) + O2(g) → H2O(g)

(Don’t forget to balance the equation!)

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Volume to Volume Calculations

How many liters of oxygen are necessary to make 5.6L of water?

H2(g) + O2(g) → H2O(g)

(Don’t forget to balance the equation!)

Now you try

CH4(g) + O2(g) → H2O(g) + CO2(g)

a.Balance the equation.

b.If 5.62L of methane react with excess oxygen, determine the theoretical yield (L) of both products.

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Try one on the Volume/Volume WS

This is homework…. Don’t forget!!

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Molecule to molecule calculations

How many molecules of H2O2 are needed to make 3.5 x 1023 molecules of water?

2H2O2 2H2O + O2

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What if you don’t start with molecules… use the flow chart!How many molecules of H2O2 are needed to

make 5.00 g of water?

2H2O2 → 2H2O + O2

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Try these!

CaCO3 + Mg → MgCO3 + Ca

a) How many molecules of Ca are produced if 39.4g of MgCO3 are also produced?

b) How many grams of Mg are necessary to react with 0.97 mol CaCO3?

Warm Up- Monday/Tuesday

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Mixed Stoichiometry Problems

CaCO3 + Mg → MgCO3 + Ca

a. How many molecules of calcium carbonate are needed to react with 5.2g of Magnesium?

b. How many grams of Ca are produced when 7.6 x 1024 atoms of magnesium react?

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Percent Yield In a perfect world, every student would get a perfect

score on every test.

Alas, we do not live in a perfect world

How do we determine the score you got on the test?

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Percent Yield (cont’d)

In a perfect world, every reaction would produce the amount of material it is supposed to.

Alas, we do not live in a perfect world.

Percent yield = the ratio comparing the amount of material actually generated in a reaction to the maximum amount possible.

Percent Yield = Actual Yield x 100

Theoretical Yield

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Percent Yield (cont’d) The theoretical yield is calculated using

stoichiometry.

The actual yield is found by experimentation.

Key Point: You can never predict the actual yield or the percent yield.

Percent Yield

2Mg + O2 → 2MgO

3.2 g of Magnesium reacted with excess oxygen. 4.9g of MgO was produced in the lab.

Calculate the percent yield.

1.Balance Equation

2.Calculate Theoretical Yield

3.Calculate % Yield

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You Try!

Sb2S3(s) + 3Fe(s) → 2Sb(s) + 3FeS(s)

When 22.3g of Sb2S3 reacts with excess of Fe, 12.7g Sb is produced in the lab. What is the percent yield?

Copper- Series 3

1. Determine the mass of the Cu(OH)2. Don’t forget to subtract the mass of the beaker and filter paper!

2. Open up the filter paper containing your product and transfer as much of the copper hydroxide as you can into the large beaker. Put the filter paper in too.

3. Add 100 ml of distilled water.

4. Put the large beaker on the hot plate and heat to a gentle boil.

5. Use forceps to remove the filter paper

6. Use the squirt bottle to rinse the filter paper.

7. Decant as much water as possible.

8. Transfer back into your beaker.

9. Allow product to settle and decant more water.

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Warm Up

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Limiting Reagent

Let’s think about a peanut butter sandwich…

The recipe calls for 2 pieces of bread and 2 Tsp. of peanut butter.

Write the reaction:

Now, we only have so much of each reactant…

Huge tube o Skippy 12 pieces of bread

How many sandwiches can we make?

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Limiting Reagent (cont’d) Chemical reactions are much the same way. The

balanced chemical equation is the recipe, telling you how much of each thing you need.

Often, chemicals are not mixed in the correct amounts, implying that one chemical will run out before the others.

The chemical that runs out first is called the limiting reagent.

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Limiting Reagent (cont’d)

Ex: 5.00g of HCl is mixed with 4.00g of NaOH according to the following reaction:

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

a)What is the limiting reagent?

b) How much of the other reactant is left over?

Limiting/Excess

You react 54.8g of silver nitrate with 22.2g of calcium chloride according to the following rxn.

AgNO3 + CaCl2 → AgCl + Ca(NO3)2

1.Balance the equation.

2.Determine the limiting.

3.Calculate the maximum amount of AgCl

4.Calculate the excess.

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